Boiler tube wearbar, stud and arc shield

ABSTRACT

Apparatus and methods for replacing or repairing missing or damaged abrasion resistant wearbars utilized in high velocity cyclone boilers. A retrofit wearbar having an aperture therein is utilized in conjunction with an end weldable stud wherein the wearbar and stud are placed in position over a damaged wearbar or against the boiler tube in the case of a missing wearbar and the stud end welding technique utilized to fuse the wearbar and stud in place with the damaged wearbar or boiler tube in the case of a missing wearbar in situ. An arc shield is utilized which has a projection from the weld fillet cavity thereof which cooperates in conjunction with the aperture of the retrofit wearbar to provide alignment of the stud in the wearbar and prevent shorting of the stud to the wearbar during the welding cycle.

BACKGROUND OF INVENTION

In such industries as power generation and particularly in large boilerapplications, the air and fuel passing across the boiler tubes withinthe boiler during entrance and combustion through the boiler can causesevere abrasion and wearing of the surface of the boiler tubes resultingin their early failure and need for replacement. One example of such ahigh wear characteristic is the cyclone boilers.

Cyclone boilers are generally very large boilers which utilize one ormore cyclones at the entrance to the boiler. The cyclones are devicesinto which extremely high velocity air and fuel are passed in a swirlingor cyclone manner around boiler tubes. Primary combustion occurs withinthe cyclone and the hot gases emerging therefrom are passed upwardlythrough the main chamber of the boiler.

In some applications, the air velocity within the cyclone can reachvelocities in the range of 600 miles per hour. This high air velocitytogether with the fuel, either oil or coal, being carried with the aircreates severe abrading action against the faces of the boiler tubesagainst which the air fuel combination directly impinges.

One manner in which the boiler tubes within the cyclone are protectedfrom the abrading action of the air fuel mixture in existing boilers isby the use of rectangular wearbars secured to the boiler tubes in aposition transverse to the direction of flow of the air fuel so as toprotect the boiler tube. FIG. 1 of the drawing illustrates the manner inwhich a plurality of wearbars 10 are secured to the exterior surface 11of a boiler tube. The wearbars 10 may be of a wear resistant materialsuch as 310 stainless steel.

During the manufacture of the cyclone portion of the boiler, thewearbars 10 are secured to the boiler tubes during fabrication.Different methods of securing the wearbars to the boiler tube sectionsduring fabrication may be utilized including resistance welding or handwelding. Fabrication by these means is relatively simple during thefabrication stage at the factory during which the various boiler tubesegments are disassembled. However, once the cyclone portion of theboiler is assembled at the plant site, the maze of boiler tubes does notreadily lend to easy access, repair and replacement of the wearbars.

During operation of the boiler, the continued impingement of the airfuel mixture against the wearbars will eventually erode the wearbars tothe point that replacement is required. Accordingly, there are periodicshutdowns of the boiler during which the cyclone is entered and thestate of the wearbars examined. Due to the different degrees ofimpingement of the air fuel mixture upon different portions of thewearbars, some of the wearbars may be only slightly worn whereas othersmay be excessively worn or even totally missing from the boiler tube. Inthose cases, either repair or replacement is necessary as the casedictates.

Disassembly of those boiler tubes having damaged wearbars is impracticaland too costly. Accordingly, the preferred course of action is to repairthe damaged wearbars in situ. Heretofore, this has been accomplished bytaking similar wearbars and handwelding them to the worn wearbars or, inthe case of missing wearbars, handwelding the wearbars to the boilertube itself. As is illustrated in FIG. 1, a replaced wearbar 13 is shownwherein handwelding by means of electric arc welding or stick welding asit is known is accomplished by means of puddling a welding pool throughan opening 14 provided in replacement wearbars as heretofore used. Thisprocedure is time consuming and thus costly.

OBJECTS AND SUMMARY OF INVENTION

It is the object of the present invention to provide a quick, economicaland efficient manner of securing wearbars to boiler tubes for repair orreplacement of damaged or missing wearbars in situ utilizing the studend welding technique.

The foregoing object is carried out in the present invention by means ofa retrofit wearbar of a configuration generally the same as the wearbarsbeing repaired or replaced. The retrofit wearbar includes an aperturetherein of generally circular configuration. An end weldable stud of adiameter slightly less than the aperture of the wearbar and adapted topass therethrough is utilized in conjunction with an arc shield topermit the wearbar and stud to be welded by the stud end weldingtechnique to the existing wearbar to be repaired or to the boiler tubein the case of a missing wearbar.

The retrofit wearbar may be flat on one face in those cases where theretrofit wearbar is welded over worn wearbars and may have a concaveconfiguration corresponding to the exterior surface of the boiler tubefor mating therewith in the case where the retrofit wearbar is used toreplace an existing but missing wearbar.

The arc shield may include a projection from the weld fillet cavitythereof which cooperates with the aperture of the retrofit wearbar toprovide alignment of the stud within the aperture to prevent shorting ofthe stud to the retrofit wearbar.

Other objects and advantages of the present invention will becomeapparent to those skilled in the art from the detailed descriptionthereof which follows.

DESCRIPTION OF DRAWING

FIG. 1 illustrates the existing wearbars and heretofore handweldedretrofit wearbars of the prior art;

FIG. 2 is an exploded perspective view of the wearbar and studcombination of the present invention for use in repairing existingwearbars;

FIG. 3 is an end perspective view of the assembly of FIG. 2 followingwelding;

FIG. 4 is an exploded perspective view of the wearbar and stud assemblyof the present invention for use in welding to a boiler tube in the caseof a missing existing wearbar;

FIG. 5 is an end sectional view of the assembly of FIG. 4 followingwelding; and

FIG. 6 is a side sectional view of the arc shield of the presentinvention.

DETAILED DESCRIPTION OF INVENTION

FIGS. 2 and 3 illustrate the embodiment of retrofit wearbar 15 utilizedfor repair of existing wearbars. The existing wearbar 16 in the case ofthe embodiment of FIGS. 2 and 3 will generally have been burned down toa point that it will not survive the next operational cycle of theboiler. However, it is not generally desired to tear the wearbars awayfrom the boiler tube 11 and thus it is preferable to weld anotherwearbar on top of the worn existing wearbar 16 to reinforce the wearbarfor the next operational cycle.

The retrofit wearbar 15 is flat on its under surface so as to generallyconform to the upper surface of the existing worn wearbar 16. Thewearbar 15 includes an aperture 17 therein generally centrally of thewearbar.

An end weldable stud 18 is provided. This stud is generally of the typeutilized in the arc stud welding technique and may include appropriateflux on the end thereof as desired. The stud 18 is of a diameter orconfiguration slightly smaller than the aperture 17 in the wearbar 15.

An arc shield 20 is provided which, during the welding operation, willsurround the stud 18 and come into engagement with the upper surface ofthe wearbar 15. The arc shield 20 includes gas vents 30 therein. The arcshield functions, in the embodiment of FIGS. 2 and 3, in the heretoforeknown manner to provide shielding of the arc from the operator and tocontain the molten metal generally within the aperture 17 and within aninner circumferential weld fillet cavity (not shown) within the arcshield 20.

The wearbar 15 is generally of a length and width and thickness similarto that of the existing wearbars 10. In this manner, the wearbar 15 mayfit between adjacent wearbars directly on top of the worn wearbar 16.Thereafter, the arc shield 20 is positioned in place over the aperture17 and the stud 18 inserted through the arc shield 20 through theaperture 17 into contact with the existing and worn wearbar 16.

The stud 18 is carried in the chunk of a conventional handheld studwelding gun. Likewise, the arc shield 20 is carried in the arc shieldholder and serves to provide the vertical spacing of the stud 18 withrespect to the wearbar 15. The welding operation is then carried out inthe normal handheld stud end welding technique wherein the stud 18contacts the surface of the existing wearbar 16, is then lifted duringan arc portion of the cycle during which contiguous portions of the studand wearbar 16 are melted and thereafter plunged into the molten pool ofmetal. The molten pool of metal, by reason of the arc, has also movedthrough a portion of the wearbar 15 and the resultant plunge creates afusion bond between the stud 18, wearbar 15 and existing wearbar 16 thusinterlocking the members together.

FIG. 3 illustrates the resultant bond of the stud 18, retrofit wearbar15 and existing wearbar 16 following the weld cycle.

FIGS. 4 and 5 illustrate the embodiment of the wearbar of the presentinvention which may be utilized to replace an existing wearbar which haseither been removed or has become disengaged from the boiler tube. Inthe embodiments of FIGS. 4 and 5, the same end weldable stud 18 and arcshield 20 are utilized. Likewise, the wearbar 21 is essentially the sameas the wearbar 15 for replacement over existing wearbars as respects itslength and width and the aperture therein but does differ on itsunderface. The underface 22 of the wearbar 21 has formed therein anarcuate or concave surface corresponding to the exterior surface of theboiler tube 11. In this manner, when the wearbar 21 is placed inposition upon the boiler tube 11, the concave surface 22 will mate withthe circular exterior surface of the boiler tube 11 and thus present atight fit. This tight fit is beneficial during the welding cycle tomaintain the molten metal within the aperture to provide a more completebond.

The stud welding apparatus and welding techniques for the embodiments ofFIGS. 4 and 5 are the same as that for FIGS. 2 and 3. Shown in FIG. 5 isthe wearbar 21 after the stud 18 has been welded in place. As may beseen from FIG. 5, the stud 18 is fusion bonded to the boiler tube 11 andalso has been fusion bonded to the wearbar 21 to provide an integratedassembly. In both of the embodiments of FIGS. 3 and 5, the arc shield 20has been removed and discarded following the welding cycle.

In FIG. 6 there is shown a modified arc shield 23 which is beneficial inuse with the wearbar and stud combination of the present invention. Thearc shield 23 includes a central bore 24 therethrough which is justslightly larger than the diameter of the stud 18. The upper portion 25of the arc shield is of a reduced diameter and is adapated to be engagedby the arc shield holder of the stud welding gun.

The lower portion of the arc shield 23 includes a horizontal shoulder 26which is adapted to engage the upper surface of the wearbar to positionthe arc shield with respect to the stud and stud welding gun. Projectinginwardly and downwardly from the shoulder 26 is a conical or frustoconical projection 27 whose greater circumference approximates thediameter of the aperture 17 within the wearbar. The projection 27permits the arc shield to readily be positioned in the aperture 17 andto center within the aperture 17. Centering of the arc shield 23 withinthe aperture automatically centers the stud 18 with respect to theaperture by reason of the concentricity of the bore 24 and theprojection 27. Centering of the stud within the aperture 17 will insureagainst arcing of the stud 18 against the walls of the aperture 17 ofthe wearbar.

The arc shield 23 further includes a weld fillet cavity 28. This weldfillet cavity functions to absorb excess molten metal moving upwardlythrough the aperture 17 during the welding cycle and to form a weldfillet around the stud 18. Additionally, the arc shield 23 includes aplurality of vents 29 positioned around the circumference of the arcshield and extending through the wall of the arc shield from theinterior to the exterior thereof. The vents 29 serve to provide a routeof escape of gases generated during welding cycle from within the arcshield to the exterior thereof while reducing and maintaining thesplatter and flash to a minimum.

By way of example in a particular embodiment, the wearbar 21 will be of3/8" thickness and 1" by 3/4" rectangle. The wearbar 15 is somewhatthinner and approximately 3/16" in thickness. Both wearbars arepreferably made of 304 stainless steel.

The stud 18 utilized as a 3/8" diameter fluxed stud formed of 430stainless steel. The aperture 17 in the wearbars is formed forapproximately 1/16" clearance each side of the stud. The arc shield 23is of a ceramic material.

From the foregoing description of the present invention, it will beappreciated that the wearbar and stud combination as well as the novelarc shield provides a quick and efficient manner by which worn ormissing wearbars may, in situ, be repaired or replaced.

The present invention has been described in respect to the particularembodiments thereof shown in the drawing and as described in thespecification. However, it is to be understood that other variations andmodifications of the invention will now become apparent to those skilledin the art by means of the foregoing disclosure of the invention andtherefore, the scope of the invention is not to be limited to theparticular embodiment shown but is to be determined in view of theappended claims.

What is claimed is:
 1. A retrofit wearbar-stud system for use in heatingapparatus employing high velocity intermixed air and fuel impinging uponmembers such as boiler tubes during combustion and wherein the membersinclude on their exterior surface a plurality of existing wearbarsproviding resistance against abrasion from the high velocity air andfuel, the wearbar system comprising, in combination:a retrofit wearbarformed of heat and abrasion resistant material and having an aperturetherein; and an end weldable stud of configuration generallycomplementary to and slightly smaller than the aperture and capable ofpassing through the aperture whereby, when the wearbar and stud areplaced in position of a damaged or missing wearbar and welded by thestud welding technique, the stud, wearbar and boiler tube or existingwearbar fuse together while the aperture at least partially filled withmolten metal.
 2. The improvements of claim 1 wherein one surface of theretrofit wearbar is complementary to the existing wearbars to permitsecuring of a retrofit wearbar over an existing worn or damaged wearbar.3. The improvement of claim 1 wherein one surface of the retrofitwearbar is of configuration complementary to the exterior configurationof the boiler tube to permit a retrofit wearbar to be secured in placeon the boiler tube to replace a missing existing wearbar.
 4. Theimprovements of claim 1 further including an arc shield surrounding theend weldable stud and having alignment means projecting from one endthereof to cooperate with the aperture in the retrofit wearbar to alignthe stud within the aperture.
 5. The improvements of claim 4 wherein thearc shield further includes vent means permitting escape of gasesgenerated during the welding of the stud.
 6. In the method of repairingheating apparatus employing high velocity intermixed air and fuelimpinging upon such members as boiler tubes during combustion andwherein the boiler tubes include on their exterior surface a pluralityof existing wearbars providing resistance against abrasion from the highvelocity air and fuel, the improvements in the method providing for insitu repair or replacement of damaged or missing wearbars comprising thesteps of:placing a retrofit wearbar having an aperture therein over theposition of the worn or missing wearbar; and placing an end weldablestud through the aperture of the wearbar in contact with the damagedwearbar or against the boiler tube and securing the retrofit wearbar inplace by the stud end welding technique utilizing sufficient weldingcurrent to, at least, partially fill the aperture of the wearbar withthe molten metal to fuse together the stud, wearbar and existing wearbaror boiler tube.
 7. The improvements of claim 6 further including thestep of utilizing an arc shield surrounding the stud and havingalignment means projecting from one end of the arc shield and extendinginto the aperture of the retrofit wearbar to align the stud within theaperture during welding thereof to prevent shorting and arcing of thestud to the wearbar.
 8. A wearbar-stud system for securing wearbars toboiler tubes and the like which boiler tubes are used in boilers,furnaces and like structures and where the wearbars protect the boilertubes from abrasion by high velocity intermixed air and fuel, thewearbar-stud system comprising:a wearbar of a prescribed thickness andparametrical edge configuration formed of heat and abrasion resistantmaterial; an aperture through the wearbar; and an end weldable stud oflength in excess of the thickness of the wearbar and of cross sectiongenerally complementary to and slightly smaller than the aperture of thewearbar whereby, when the wearbar is placed upon a boiler tube or anexisting wearbar and the stud inserted into the aperture and studwelded, the aperture at least partially fills with molten metal tosubstantially fuse the stud, wearbar and boiler tube or existing wearbarone to another to thus secure the wearbar in place.
 9. The wearbar-studsystem of claim 8 further including an arc shield adapted to bepositioned around the end weldable stud and having alignment meansprojecting from one end thereof to cooperate with the aperture in thewearbar to align the studs within the aperture of the wearbar.
 10. Thewearbar-stud system of claim 9 wherein the arc shield further includesvent means permitting escape of gases generated during the welding ofthe end weldable stud.
 11. The wearbar-stud system of either claims 8 or9 wherein the wearbar is of substantially uniform thickness and onesurface thereof is complementary to the existing wearbars to which thewearbar is to be secured to permit securing of wearbars over existingworn or damaged wearbars.
 12. The wearbar-stud system of either claims 8or 9 wherein one surface of the wearbar is flat and the opposing surfacethereof includes a portion thereof of configuration complementary to theexterior configuration of the boiler tube to which the wearbar is to besecured to permit the wearbar to be secured in place on new boiler tubesor to replace a missing wearbar on pre-existing boiler tubes.
 13. Themethod of securing wearbars to members such as boiler tubes used infurnaces and the like wherein the wearbars protect the boiler tubes fromabrasion by high velocity air and fuel comprising the steps of:placing awearbar having an aperture therein in position upon the boiler tube; andplacing an end weldable stud through the aperture of the wearbar incontact with the boiler tube and securing the wearbar in place by studwelding the stud by the stud welding technique utilizing sufficientwelding current to, at least, partially fill the aperture of the wearbarwith molten metal to fuse together the stud, wearbar and boiler tube.14. The method of claim 13 further including the step of utilizing anarc shield surrounding the stud and having alignment means projectingfrom one end of the arc shield and extending into the aperture of thewearbar to align the stud within the aperture during welding thereof toprevent shorting and arcing of the stud to the wearbar.